King, who caucuses in the U.S. Senate with Democrats, appeared with Collins on Friday at the Skowhegan, Maine, library named for Margaret Chase Smith, one of the state's most revered political figures and a mentor to Collins.

"I think she's one of the Senate's MVPs — smart, tough, and always willing to listen. In my book, she's a model senator, and I'm delighted to support her re-election," King said of Collins in a statement to The Associated Press.

Because Collins is expected to breeze to her fourth Senate term — her Democratic opponent, Shenna Bellows, ran Maine's ACLU chapter — the endorsement may draw more attention to King.

"King’s move could foreshadow his own political plans in the next Congress," The Hill reported, noting that "the senator hasn’t ruled out aligning himself with Republicans if they end up controlling the Senate."

This is King's first endorsement of Collins. The two previously squared off in 1994, when King bested Collins and another candidate to become governor of Maine.

In the Senate, they've been a model of home-state cooperation in everything from military contracting to budget negotiations.

"She always puts Maine and the country first and isn't afraid to cross party lines to get things done," King said in his statement.